Declines of species in fragmented landscapes can potentially be reversed either by restoring conn... more Declines of species in fragmented landscapes can potentially be reversed either by restoring connectivity or restoring local habitat quality. Models fitted to snapshot occupancy data can be used to predict the effectiveness of these actions. However, such inferences can be misleading if the reliability of the habitat and landscape metrics used is unknown. The only way to unambiguously resolve the roles of habitat quality and metapopulation dynamics is to conduct experimental reintroductions to unoccupied patches, allowing habitat quality to be measured directly from data on vital rates. We therefore conducted a 15-year study that involved reintroducing a threatened New Zealand bird species to unoccupied forest fragments to obtain reliable data on their habitat quality, and re-assess initial inferences made by modelling occupancy against habitat and landscape metrics. While reproductive rates were similar among fragments, subtle differences in adult survival rates resulted in λ (finite rate of increase) being estimated to be < 0.9 for 9 of the 12 fragments that were previously unoccupied whereas this was the case for only 1 of 14 naturally occupied fragments. This variation in λ largely explained the original occupancy pattern, reversing our original conclusion that this occupancy pattern was isolation driven, and suggesting that it would be detrimental to increase connectivity without improving local habitat quality. These results illustrate that inferences from snapshot occupancy should be treated with caution and subjected to testing through experimental reintroductions in selected model systems. This article is protected by copyright. All rights reserved.
max N min f , where f (typically between 0.1 and 0.5) is a "recovery factor" that may be set lowe... more max N min f , where f (typically between 0.1 and 0.5) is a "recovery factor" that may be set lower to allow a population to recover faster, or to provide additional protection to the population. If the human-caused mortalities are less than the PBR, then a depleted population will be able to recover so that, given sufficient time, it has a 95% probability of being over half the carrying capacity. When assessing the potential impact of human-caused mortalities on seabird populations, the PBR has been used as a guide to the productivity of the seabird populations. Applying the PBR to seabirds is difficult as neither the maximum growth rate nor the total population size can be directly measured. Instead, approximations must be used that allow estimation of these parameters from readily available data. In this report, we used simulations of seabird demography to assess the accuracy of these approximations. This approach involved three main steps. First, we simulated the population dynamics for 12 types of seabirds, representing a range of species breeding in New Zealand. For each species type, we estimated the maximum human-caused mortality rate that the populations could incur, while still being able to recover to above half the carrying capacity, with 95% probability, in the presence of both environmental and demographic stochasticity. Second, we generated a PBR estimate using an approximate maximum growth rate and population size. The PBR estimate included a parameter ρ, calibrated so that the base PBR (PBR b ; evaluated with f = 1 and with the total population, N, rather than the conservative estimate, N min) had only a 5%-probability of exceeding the maximum human-caused mortality. Finally, we explored the effect of errors or bias in the demographic parameters used for the calculation of the PBR, to provide guidance in setting the value of the recovery factor, f. The analysis showed that the approximate base PBR derived from demographic parameter estimates tended to overestimate the maximum human-caused mortality. Inclusion of a calibration factor, ρ, was required to adjust the PBR approximations to meet the management criterion; ρ varied between 0.17 and 0.61, depending on the species types. In general, the calibration factor was smaller for species with slower growth rates, such as albatrosses, and higher for species with higher growth rates, such as shags and penguins. Previous estimates of the PBR for seabird populations that did not include this calibration factor are likely to have overestimated the human-caused mortalities that the populations could incur. The choice of f values will depend on what errors in the underlying parameters are considered plausible, and on requirements for the recovery time of depleted populations. In this report, some exploration of the consequences of incorrect estimates of the parameters is given, but an explicit recommendation for the choice of f values is not made. With the inclusion of the additional calibration factor, ρ, the method for calculating the PBR described here provides a simple way for determining whether fishing-related mortalities are sufficiently low that seabird populations are able to recover to and/or remain at above half the carrying capacity in the long term. Ministry for Primary Industries Application of Potential Biological Removal methods to seabird populations • 1 Ministry for Primary Industries Application of Potential Biological Removal methods to seabird populations • 3
Responsible fisheries management requires the consideration of fishing effects on ecosystems incl... more Responsible fisheries management requires the consideration of fishing effects on ecosystems including non-target species. Extensive distributional overlap between fisheries and seabirds, and the attractiveness of the catch and fishery waste to foraging birds, leads to fatal interactions between seabirds and fishing gear. In a series of experiments, we have investigated measures for managing trawl processing waste to reduce seabird mortalities. Different fisheries generate different volumes of processing waste, and vessel capacities for holding this waste can vary significantly both within and between trawl fleets. Here, we compare seabird responses to discharging trawl fisheries waste ad hoc, as and when waste became available, with responses to discharging waste after holding periods of 30 min and 2 h. Using abundance as a proxy for the risk of mortality, we show that compared to discharging ad hoc, holding waste for two specified periods prior to discharge significantly reduces vessel attendance by small seabirds, and both small and large seabirds, respectively. Drawing on this study and our past work, we provide best practice guidelines for trawler waste management to reduce seabird mortality due to interactions with trawl warps. If the ideal approach of discharging waste only when fishing gear is out of the water is impossible, then discharging waste rapidly in maximally large batches, as infrequently as possible is recommended. Holding periods of 30 min to 8 h may be required to reduce the abundance of small species of seabirds attending vessels. For large seabirds, holding periods of 2-4 h are required, and 8 h holding periods are still more effective. Discharging waste as it becomes available is not recommended. Mincing processing waste can reduce the attendance of some seabird species at vessels, especially large albatrosses. However, holding waste is preferred, due to relative simplicity in the mechanics of dealing with waste, lower cost, and greater reductions in seabird abundance. Though developed on trawl fisheries, principles of these guidelines are applicable to any fishery discharging waste attractive to seabirds. While holding fisheries waste can minimise seabird captures on trawl warps worldwide, evidence-based management measures are still required to reduce seabird mortalities in trawl nets.
Demographic rates, such as annual survival rate, are generally difficult to estimate for long-liv... more Demographic rates, such as annual survival rate, are generally difficult to estimate for long-lived seabirds, because of the length of time required for this kind of study and the remoteness of colonies. However, a small colony of northern royal albatross (Diomedea sanfordi) established itself on the mainland of New Zealand at Taiaroa Head, making possible regular banding and monitoring of its individuals since the first chick fledged, in 1938. Data on the presence/absence of birds, as well as on breeding outcomes, were available for the period from 1989-90 to 2011-12, and included 2128 annual resightings of 355 banded individuals of known age. The main goal of the present study was to estimate the annual survival rate of juveniles, pre-breeders, and adults at Taiaroa Head. These rates were estimated simultaneously in a single Bayesian multi-state capture-recapture model. Several models were fitted to the data, with different levels of complexity. From the most parsimonious model, the overall annual adult survival rate was estimated as 0.950 (95% c.i.: 0.941-0.959). In this model, adult survival declined with age, from 0.976 (95% c.i.: 0.963-0.988) at 6 years, the minimum age at first breeding, to 0.915 (95% c.i.: 0.879-0.946) at 40 years. Mean annual survival of pre-breeders was 0.966 (95% c.i.: 0.950-0.980), and 0.933 (95% c.i.: 0.908-0.966) for juveniles. There was no discernible difference in survival between males and females, and there was no apparent trend in survival over time. Estimates of other demographic rates were also obtained during the estimation process. The mean age at first return of juveniles to the colony was estimated as 4.8 years (95% c.i.: 4.6-5.1), and the mean age at first breeding as 8.9 years (95% c.i.: 8.5-9.3). Because all the birds of the colony were banded, it was possible to estimate the total population size. The number of northern royal albatross present annually at the Taiaroa Head colony has doubled since 1989-90, and the current total population size was estimated to be over 200 individuals. The ratio of the total population size to the number of annual breeding pairs varied from 5 to 12 among years, with an overall mean of 7.65 (95% c.i.: 7.56-7.78), and this high variability highlights the need for a sufficient number of surveys of seabird breeding populations before reliable conclusions on population trends can be made. Although long-term data allowed estimates of demographic rates of northern royal albatross at Taiaroa Head, the location of the colony and the ongoing management by staff mean that the population dynamics may differ from those of the main population on the Chatham Islands.
1. The identification of geographic areas where the densities of animals are highest across their... more 1. The identification of geographic areas where the densities of animals are highest across their annual cycles is a crucial step in conservation planning. In marine environments, however, it can be particularly difficult to map the distribution of species, and the methods used are usually biased towards adults, neglecting the distribution of other life-history stages even though they can represent a substantial proportion of the total population. 2. Here we develop a methodological framework for estimating populationlevel density distributions of seabirds, integrating tracking data across the main | 515
Seabirds are globally threatened. In the face of multiple threats, it is critical to understand h... more Seabirds are globally threatened. In the face of multiple threats, it is critical to understand how conservation strategies that mitigate one threat intersect with others to impact population viability. Marine threats, including pollution, climate change, and fisheries could derail gains to seabird populations resulting from arduous predator eradication efforts. However, this potentially negative effect is yet to be evaluated. We test whether mortality from marine threats can subvert the on-going recovery of 17 seabird species from 37 colonies on islands worldwide where predators were removed. We use demographic modelling to estimate potential adult mortality from fisheries, plastic ingestion, and climate change. For 82% of the species we examine, marine threats do not impede recovery following predator eradication. However, for six colonies of three species, Calonectris diomedea, C. borealis, and Ardenna carneipes, mortality from multiple marine threats may interrupt their recovery...
Managed pine plantations now constitute a large portion of mainland New Zealand. Despite many nat... more Managed pine plantations now constitute a large portion of mainland New Zealand. Despite many native birds inhabiting these exotic habitats, their value for biodiversity conservation is unclear. Although numerous studies have quantified densities of native bird species in pine plantations, it is unknown whether these individuals constitute self-sustaining populations. Here we address this question for North Island robins (Petroica longipes) in a Pinus radiata plantation in the central North Island. We compare survival and reproduction data of robins collected in three different compartments of the plantation from 2003-2005 to similar data collected from 20 unmanaged native forest fragments from 2002-2014. We used the data to derive estimates of finite rate of increase (λ) using a Bayesian hierarchical modelling framework that accounted for site-to-site and temporal variation. The mean reproduction rate was much lower in the pine plantation, with females producing 0.34 (SE 0.15) independent juveniles per year, in comparison to 1.02 (SE 0.21) in fenced native fragments and 0.83 (SE 0.21) in grazed native fragments. These differences are attributable to lower nest survival, as nests in the pines had a 0.09 (SE 0.05) probability of surviving to fledging, compared to 0.33 (SE 0.04) for fenced native fragments and 0.28 (SE 0.06) for grazed native fragments. In contrast, the mean adult female survival probability was 0.64 (SE 0.13) in the pines in comparison to 0.55 (SE 0.04) in the native fragments. The λ estimate for the pine plantation was 0.76 (SE 0.14), meaning λ was unlikely to be >1 as is required for a self-sustaining population. The mean λ was estimated to be 0.89 (SE 0.09) for fenced native fragments and 0.83 (SE 0.09) for unfenced native fragments, but varied among fragments with estimates close to 1 for some fenced fragments. Therefore, the pine plantation probably constituted sink habitat that retained robins due to immigration from the surrounding landscape, whereas at least some of the native fragments could potentially be self-sustaining.
Forest fragments have biodiversity value that may be enhanced through management such as control ... more Forest fragments have biodiversity value that may be enhanced through management such as control of non-native predators. However, such efforts may be ineffective, and research is needed to ensure that predator control is done strategically. We used Bayesian hierarchical modeling to estimate fragmentspecific effects of experimental rat control on a native species targeted for recovery in a New Zealand pastoral landscape. The experiment was a modified BACI (before-after-control-impact) design conducted over 6 years in 19 forest fragments with low-density subpopulations of North Island Robins (Petroica longipes). The aim was to identify individual fragments that not only showed clear benefits of rat control, but also would have a high probability of subpopulation growth even if they were the only fragment managed. We collected data on fecundity, adult and juvenile survival, and juvenile emigration, and modeled the data in an integrated framework to estimate the expected annual growth rate (λ) of each subpopulation with and without rat control. Without emigration, subpopulation growth was estimated as marginal (λ = 0.95-1.05) or negative (λ = 0.74-0.90) without rat control, but it was estimated as positive in all fragments (λ = 1.4-2.1) if rats were controlled. This reflected a 150% average increase in fecundity and 45% average increase in adult female survival. The probability of a juvenile remaining in its natal fragment was 0.37 on average, but varied with fragment connectivity. With juvenile emigration added, 6 fragments were estimated to have a high (>0.8) probability of being self-sustaining (λ > 1) with rat control. The key factors affecting subpopulation growth rates under rat control were low connectivity and stock fencing because these factors were associated with lower juvenile emigration and higher fecundity, respectively. However, there was also substantial random variation in adult survival among fragments, illustrating the importance of hierarchical modeling for fragmentation studies.
Dispersal from release areas is a critical problem for reintroductions. Reliable methods are ther... more Dispersal from release areas is a critical problem for reintroductions. Reliable methods are therefore needed for analysing post-release monitoring data to guide further releases. Radio tracking can greatly improve data quality by distinguishing dispersal from mortality. However, fates of animals continue to be uncertain if transmitters have short battery life and detection range, as is typically the case with small animals. We present an approach for simultaneously modelling probabilities of fidelity (remaining in release area), survival, detection and transmitter failure from post-release monitoring data, and illustrate how it was applied to translocations of North Island robins (Petroica longipes) to 17 forest fragments (5-56 ha) over 5 years. The modelling showed that fidelity probability depended on the sex (higher in females) and translocation date (higher in winter than autumn), and that variation among fragments was well explained by the ''cost distance to nearest neighbour'' (an index reflecting the amount of pasture and shrubland needing to be crossed to reach another forest area) and the area of the release fragment (higher in larger fragments). Combined with survival, the estimated probability of a bird remaining in its release fragment the next breeding season ranged from 0.02 to 0.39. As these estimates were refined, they could be used to assess suitability of fragments for further releases and numbers of each sex needing to be released to compensate for dispersal. The Bayesian framework underlying the approach potentially allows application to any amount of data by using informative priors derived from previous translocations or expert opinion.
In a recent risk assessment, northern royal albatross was identified as one the seabird species m... more In a recent risk assessment, northern royal albatross was identified as one the seabird species most at risk from incidental captures in commercial fisheries in New Zealand. The uncertainty of the estimated risk was large, owing to its sensitivity to the uncertainty surrounding existing estimates of the annual survival rate. This highlights the need for accurate demographic measures of this species. Demographic rates, such as the annual survival rate, are generally difficult to estimate for long-lived seabirds such as northern royal albatross, because of the length of the study required and the remoteness of colonies.
Declines of species in fragmented landscapes can potentially be reversed either by restoring conn... more Declines of species in fragmented landscapes can potentially be reversed either by restoring connectivity or restoring local habitat quality. Models fitted to snapshot occupancy data can be used to predict the effectiveness of these actions. However, such inferences can be misleading if the reliability of the habitat and landscape metrics used is unknown. The only way to unambiguously resolve the roles of habitat quality and metapopulation dynamics is to conduct experimental reintroductions to unoccupied patches, allowing habitat quality to be measured directly from data on vital rates. We therefore conducted a 15-year study that involved reintroducing a threatened New Zealand bird species to unoccupied forest fragments to obtain reliable data on their habitat quality, and re-assess initial inferences made by modelling occupancy against habitat and landscape metrics. While reproductive rates were similar among fragments, subtle differences in adult survival rates resulted in λ (finite rate of increase) being estimated to be < 0.9 for 9 of the 12 fragments that were previously unoccupied whereas this was the case for only 1 of 14 naturally occupied fragments. This variation in λ largely explained the original occupancy pattern, reversing our original conclusion that this occupancy pattern was isolation driven, and suggesting that it would be detrimental to increase connectivity without improving local habitat quality. These results illustrate that inferences from snapshot occupancy should be treated with caution and subjected to testing through experimental reintroductions in selected model systems. This article is protected by copyright. All rights reserved.
max N min f , where f (typically between 0.1 and 0.5) is a "recovery factor" that may be set lowe... more max N min f , where f (typically between 0.1 and 0.5) is a "recovery factor" that may be set lower to allow a population to recover faster, or to provide additional protection to the population. If the human-caused mortalities are less than the PBR, then a depleted population will be able to recover so that, given sufficient time, it has a 95% probability of being over half the carrying capacity. When assessing the potential impact of human-caused mortalities on seabird populations, the PBR has been used as a guide to the productivity of the seabird populations. Applying the PBR to seabirds is difficult as neither the maximum growth rate nor the total population size can be directly measured. Instead, approximations must be used that allow estimation of these parameters from readily available data. In this report, we used simulations of seabird demography to assess the accuracy of these approximations. This approach involved three main steps. First, we simulated the population dynamics for 12 types of seabirds, representing a range of species breeding in New Zealand. For each species type, we estimated the maximum human-caused mortality rate that the populations could incur, while still being able to recover to above half the carrying capacity, with 95% probability, in the presence of both environmental and demographic stochasticity. Second, we generated a PBR estimate using an approximate maximum growth rate and population size. The PBR estimate included a parameter ρ, calibrated so that the base PBR (PBR b ; evaluated with f = 1 and with the total population, N, rather than the conservative estimate, N min) had only a 5%-probability of exceeding the maximum human-caused mortality. Finally, we explored the effect of errors or bias in the demographic parameters used for the calculation of the PBR, to provide guidance in setting the value of the recovery factor, f. The analysis showed that the approximate base PBR derived from demographic parameter estimates tended to overestimate the maximum human-caused mortality. Inclusion of a calibration factor, ρ, was required to adjust the PBR approximations to meet the management criterion; ρ varied between 0.17 and 0.61, depending on the species types. In general, the calibration factor was smaller for species with slower growth rates, such as albatrosses, and higher for species with higher growth rates, such as shags and penguins. Previous estimates of the PBR for seabird populations that did not include this calibration factor are likely to have overestimated the human-caused mortalities that the populations could incur. The choice of f values will depend on what errors in the underlying parameters are considered plausible, and on requirements for the recovery time of depleted populations. In this report, some exploration of the consequences of incorrect estimates of the parameters is given, but an explicit recommendation for the choice of f values is not made. With the inclusion of the additional calibration factor, ρ, the method for calculating the PBR described here provides a simple way for determining whether fishing-related mortalities are sufficiently low that seabird populations are able to recover to and/or remain at above half the carrying capacity in the long term. Ministry for Primary Industries Application of Potential Biological Removal methods to seabird populations • 1 Ministry for Primary Industries Application of Potential Biological Removal methods to seabird populations • 3
Responsible fisheries management requires the consideration of fishing effects on ecosystems incl... more Responsible fisheries management requires the consideration of fishing effects on ecosystems including non-target species. Extensive distributional overlap between fisheries and seabirds, and the attractiveness of the catch and fishery waste to foraging birds, leads to fatal interactions between seabirds and fishing gear. In a series of experiments, we have investigated measures for managing trawl processing waste to reduce seabird mortalities. Different fisheries generate different volumes of processing waste, and vessel capacities for holding this waste can vary significantly both within and between trawl fleets. Here, we compare seabird responses to discharging trawl fisheries waste ad hoc, as and when waste became available, with responses to discharging waste after holding periods of 30 min and 2 h. Using abundance as a proxy for the risk of mortality, we show that compared to discharging ad hoc, holding waste for two specified periods prior to discharge significantly reduces vessel attendance by small seabirds, and both small and large seabirds, respectively. Drawing on this study and our past work, we provide best practice guidelines for trawler waste management to reduce seabird mortality due to interactions with trawl warps. If the ideal approach of discharging waste only when fishing gear is out of the water is impossible, then discharging waste rapidly in maximally large batches, as infrequently as possible is recommended. Holding periods of 30 min to 8 h may be required to reduce the abundance of small species of seabirds attending vessels. For large seabirds, holding periods of 2-4 h are required, and 8 h holding periods are still more effective. Discharging waste as it becomes available is not recommended. Mincing processing waste can reduce the attendance of some seabird species at vessels, especially large albatrosses. However, holding waste is preferred, due to relative simplicity in the mechanics of dealing with waste, lower cost, and greater reductions in seabird abundance. Though developed on trawl fisheries, principles of these guidelines are applicable to any fishery discharging waste attractive to seabirds. While holding fisheries waste can minimise seabird captures on trawl warps worldwide, evidence-based management measures are still required to reduce seabird mortalities in trawl nets.
Demographic rates, such as annual survival rate, are generally difficult to estimate for long-liv... more Demographic rates, such as annual survival rate, are generally difficult to estimate for long-lived seabirds, because of the length of time required for this kind of study and the remoteness of colonies. However, a small colony of northern royal albatross (Diomedea sanfordi) established itself on the mainland of New Zealand at Taiaroa Head, making possible regular banding and monitoring of its individuals since the first chick fledged, in 1938. Data on the presence/absence of birds, as well as on breeding outcomes, were available for the period from 1989-90 to 2011-12, and included 2128 annual resightings of 355 banded individuals of known age. The main goal of the present study was to estimate the annual survival rate of juveniles, pre-breeders, and adults at Taiaroa Head. These rates were estimated simultaneously in a single Bayesian multi-state capture-recapture model. Several models were fitted to the data, with different levels of complexity. From the most parsimonious model, the overall annual adult survival rate was estimated as 0.950 (95% c.i.: 0.941-0.959). In this model, adult survival declined with age, from 0.976 (95% c.i.: 0.963-0.988) at 6 years, the minimum age at first breeding, to 0.915 (95% c.i.: 0.879-0.946) at 40 years. Mean annual survival of pre-breeders was 0.966 (95% c.i.: 0.950-0.980), and 0.933 (95% c.i.: 0.908-0.966) for juveniles. There was no discernible difference in survival between males and females, and there was no apparent trend in survival over time. Estimates of other demographic rates were also obtained during the estimation process. The mean age at first return of juveniles to the colony was estimated as 4.8 years (95% c.i.: 4.6-5.1), and the mean age at first breeding as 8.9 years (95% c.i.: 8.5-9.3). Because all the birds of the colony were banded, it was possible to estimate the total population size. The number of northern royal albatross present annually at the Taiaroa Head colony has doubled since 1989-90, and the current total population size was estimated to be over 200 individuals. The ratio of the total population size to the number of annual breeding pairs varied from 5 to 12 among years, with an overall mean of 7.65 (95% c.i.: 7.56-7.78), and this high variability highlights the need for a sufficient number of surveys of seabird breeding populations before reliable conclusions on population trends can be made. Although long-term data allowed estimates of demographic rates of northern royal albatross at Taiaroa Head, the location of the colony and the ongoing management by staff mean that the population dynamics may differ from those of the main population on the Chatham Islands.
1. The identification of geographic areas where the densities of animals are highest across their... more 1. The identification of geographic areas where the densities of animals are highest across their annual cycles is a crucial step in conservation planning. In marine environments, however, it can be particularly difficult to map the distribution of species, and the methods used are usually biased towards adults, neglecting the distribution of other life-history stages even though they can represent a substantial proportion of the total population. 2. Here we develop a methodological framework for estimating populationlevel density distributions of seabirds, integrating tracking data across the main | 515
Seabirds are globally threatened. In the face of multiple threats, it is critical to understand h... more Seabirds are globally threatened. In the face of multiple threats, it is critical to understand how conservation strategies that mitigate one threat intersect with others to impact population viability. Marine threats, including pollution, climate change, and fisheries could derail gains to seabird populations resulting from arduous predator eradication efforts. However, this potentially negative effect is yet to be evaluated. We test whether mortality from marine threats can subvert the on-going recovery of 17 seabird species from 37 colonies on islands worldwide where predators were removed. We use demographic modelling to estimate potential adult mortality from fisheries, plastic ingestion, and climate change. For 82% of the species we examine, marine threats do not impede recovery following predator eradication. However, for six colonies of three species, Calonectris diomedea, C. borealis, and Ardenna carneipes, mortality from multiple marine threats may interrupt their recovery...
Managed pine plantations now constitute a large portion of mainland New Zealand. Despite many nat... more Managed pine plantations now constitute a large portion of mainland New Zealand. Despite many native birds inhabiting these exotic habitats, their value for biodiversity conservation is unclear. Although numerous studies have quantified densities of native bird species in pine plantations, it is unknown whether these individuals constitute self-sustaining populations. Here we address this question for North Island robins (Petroica longipes) in a Pinus radiata plantation in the central North Island. We compare survival and reproduction data of robins collected in three different compartments of the plantation from 2003-2005 to similar data collected from 20 unmanaged native forest fragments from 2002-2014. We used the data to derive estimates of finite rate of increase (λ) using a Bayesian hierarchical modelling framework that accounted for site-to-site and temporal variation. The mean reproduction rate was much lower in the pine plantation, with females producing 0.34 (SE 0.15) independent juveniles per year, in comparison to 1.02 (SE 0.21) in fenced native fragments and 0.83 (SE 0.21) in grazed native fragments. These differences are attributable to lower nest survival, as nests in the pines had a 0.09 (SE 0.05) probability of surviving to fledging, compared to 0.33 (SE 0.04) for fenced native fragments and 0.28 (SE 0.06) for grazed native fragments. In contrast, the mean adult female survival probability was 0.64 (SE 0.13) in the pines in comparison to 0.55 (SE 0.04) in the native fragments. The λ estimate for the pine plantation was 0.76 (SE 0.14), meaning λ was unlikely to be >1 as is required for a self-sustaining population. The mean λ was estimated to be 0.89 (SE 0.09) for fenced native fragments and 0.83 (SE 0.09) for unfenced native fragments, but varied among fragments with estimates close to 1 for some fenced fragments. Therefore, the pine plantation probably constituted sink habitat that retained robins due to immigration from the surrounding landscape, whereas at least some of the native fragments could potentially be self-sustaining.
Forest fragments have biodiversity value that may be enhanced through management such as control ... more Forest fragments have biodiversity value that may be enhanced through management such as control of non-native predators. However, such efforts may be ineffective, and research is needed to ensure that predator control is done strategically. We used Bayesian hierarchical modeling to estimate fragmentspecific effects of experimental rat control on a native species targeted for recovery in a New Zealand pastoral landscape. The experiment was a modified BACI (before-after-control-impact) design conducted over 6 years in 19 forest fragments with low-density subpopulations of North Island Robins (Petroica longipes). The aim was to identify individual fragments that not only showed clear benefits of rat control, but also would have a high probability of subpopulation growth even if they were the only fragment managed. We collected data on fecundity, adult and juvenile survival, and juvenile emigration, and modeled the data in an integrated framework to estimate the expected annual growth rate (λ) of each subpopulation with and without rat control. Without emigration, subpopulation growth was estimated as marginal (λ = 0.95-1.05) or negative (λ = 0.74-0.90) without rat control, but it was estimated as positive in all fragments (λ = 1.4-2.1) if rats were controlled. This reflected a 150% average increase in fecundity and 45% average increase in adult female survival. The probability of a juvenile remaining in its natal fragment was 0.37 on average, but varied with fragment connectivity. With juvenile emigration added, 6 fragments were estimated to have a high (>0.8) probability of being self-sustaining (λ > 1) with rat control. The key factors affecting subpopulation growth rates under rat control were low connectivity and stock fencing because these factors were associated with lower juvenile emigration and higher fecundity, respectively. However, there was also substantial random variation in adult survival among fragments, illustrating the importance of hierarchical modeling for fragmentation studies.
Dispersal from release areas is a critical problem for reintroductions. Reliable methods are ther... more Dispersal from release areas is a critical problem for reintroductions. Reliable methods are therefore needed for analysing post-release monitoring data to guide further releases. Radio tracking can greatly improve data quality by distinguishing dispersal from mortality. However, fates of animals continue to be uncertain if transmitters have short battery life and detection range, as is typically the case with small animals. We present an approach for simultaneously modelling probabilities of fidelity (remaining in release area), survival, detection and transmitter failure from post-release monitoring data, and illustrate how it was applied to translocations of North Island robins (Petroica longipes) to 17 forest fragments (5-56 ha) over 5 years. The modelling showed that fidelity probability depended on the sex (higher in females) and translocation date (higher in winter than autumn), and that variation among fragments was well explained by the ''cost distance to nearest neighbour'' (an index reflecting the amount of pasture and shrubland needing to be crossed to reach another forest area) and the area of the release fragment (higher in larger fragments). Combined with survival, the estimated probability of a bird remaining in its release fragment the next breeding season ranged from 0.02 to 0.39. As these estimates were refined, they could be used to assess suitability of fragments for further releases and numbers of each sex needing to be released to compensate for dispersal. The Bayesian framework underlying the approach potentially allows application to any amount of data by using informative priors derived from previous translocations or expert opinion.
In a recent risk assessment, northern royal albatross was identified as one the seabird species m... more In a recent risk assessment, northern royal albatross was identified as one the seabird species most at risk from incidental captures in commercial fisheries in New Zealand. The uncertainty of the estimated risk was large, owing to its sensitivity to the uncertainty surrounding existing estimates of the annual survival rate. This highlights the need for accurate demographic measures of this species. Demographic rates, such as the annual survival rate, are generally difficult to estimate for long-lived seabirds such as northern royal albatross, because of the length of the study required and the remoteness of colonies.
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